This application is a 371 national stage application of International Patent Application No. PCT/EP99/00003, filed on Jan. 4, 1999, which has priority benefit of Italian Patent Application No. M198A000021, filed on Jan. 9,1998.
1. Field of the Invention
The present invention relates to a process for selective hydrogenation of maleic or succinic anhydride to gamma-butyrolactone (GBL) in the vapor phase using a catalyst comprising a mixed oxide of copper and zinc.
2. Background Art
The present invention relates to a process for selective hydrogenation of maleic or succinic anhydride to gamma-butyrolactone (GBL) in the Sapour phase using a catalyst comprising a mixed oxide of copper and zinc
GBL represents an example of a small volume commodity of great industrial interest, because of its increasing demand.
The main use of GBL is as intermediate for the synthesis of solvents with lower environmental impact than chlorinated ones, like pyrrolidone and N-methylpyrrolidone. It is also the raw material for the production of N-vinilpyrrolidone, of herbicides, pharmaceuticals and rubber additives.
The first works on GBL synthesis appeared in the 1940's, due to the start up of the Reppe process from acetylene and formaldehyde to give 1,4 butanediol (BDO) and then GBL by dehydrogenation. The drawbacks of this process are connected with the fluctuating prices of the raw materials and, mainly, with the hazard and the environmental impact of the use of both acetylene and formaldehyde.
During the second half of this century, other technologies have been studied and the number of patents about GBL production processes alternative to the Reppe process constantly increased.
The availability of maleic anhydride on industrial scale led to the development of new technologies for producing GBL, tetrahydrofurane (THF) or BDO by hydrogenation of maleic anhydride or of maleic anhydride derivatives like maleic acid diesters or succinic anhydride.
The liquid phase hydrogenation of maleic anhydride to GBL has been employed in commercial production, but never reached great industrial importance.
Many patents describe the vapor phase hydrogenation of maleic anhydride or its esters, but mainly for the production of BDO; for instance, WO 86/03189 describe the vapor phase hydrogenation of diethyl maleate to BDO. WO 86/07358 describes a similar process for GBL production.
From a technological and economical point of view the esters of maleic acid or other maleic acid and/or succinic acid derivatives are less desirable raw materials compared with maleic anhydride.
Many patents describe the direct vapor phase hydrogenation of maleic anhydride to GBL, but none of the processes disclosed are completely satisfactory.
Some of these patents claim the use of copper chromites as catalysts (e.g. U.S. Pat. No. 3,065,243) but with unsatisfactory conversion and selectivity. Similar systems were claimed in U.S. Pat. No. 3,580,930 or in EP 332 140 (Cu/Zn/Cr/Al), but none of them are completely satisfactory in terns of GBL yield, productivity, by-products formation and catalyst durability. Moreover chromium containing catalysts should not be the choice because of the negative environment impact of chromium, due to the toxicity of its compounds.
The WO 91/16132 disclose a process for the GBL production from maleic anhydride using a Cu/Zn/Al catalyst calcined at 400-525.degree.C. Such a high temperature is a draw-back in terms of plant design and operation. Different catalytic systems, based on noble metal catalysts such as Cu/Pd and Cu/Pt have been described in e.g. U.S. Pat. No. 4,105,674. The cost of the noble metal is the draw back of these catalysts.